Stability-constrained allocation of grid-forming and grid-following energy storage in weakly interconnected power grids

With increasing renewable energy penetration, the degree of power-electronics dominance in weakly interconnected power systems is steadily rising, accompanied by a declining share of synchronous generators and reduced disturbance resilience. Once the tie line faults, the system is prone to unintentional islanding, posing risks to power supply reliability and operational stability. Grid-forming energy storage (GFM-ESS) combines active grid-forming support with power regulation capability, making it effective in mitigating the operational risks for weakly interconnected power grids. Therefore, this paper proposes a stability-constrained capacity allocation strategy for GFM-ESS and grid-following energy storage systems (GFL-ESS) in weakly interconnected power systems, with consideration of frequency and voltage stability under grid-connected and islanded conditions. Firstly, a quantitative metric is proposed to characterize the instantaneous support capability of GFM-ESS and integrated with existing stability metrics to assess the system’s support requirements of GFM-ESS. Secondly, genetic algorithm (GA) is coupled with the commercial Power System Analysis Software Package (PSASP) time-domain simulations to evaluate the metrics and perform iterative optimization. Given the total ESS capacity requirement predetermined from an economic assessment, the objective is to determine the minimum GFM-ESS capacity required to maintain system frequency and voltage stability, while incorporating penalty terms of stability-constrained violations. This formulates a coordinated allocation model for GFL-ESS and GFM-ESS considering both steady-state and short-term stability support requirements. Finally, a case study of a practical county-level grid in China verifies the validity of the proposed metrics in capturing dynamic support capability and confirms the effectiveness of the proposed allocation method.